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The synthesis of ZnO particles from Zn(CH3Co2) in 2-propanol as a function of the concentration of water is reported. Particles with diameters of 3-5 nm are formed depending on time, temperature, and water concentration.

The study demonstrated that alternative redox mediators could be successfully used within dye-sensitized solar cells comprised of a nanocrystalline SnO(sub 2) electrode. Photocurrent efficiencies and cell voltages were larger using the alternative redox mediator (SeCN)2/SeCN(super -) compared to I(sub 3)(super -)/I(super -) for all three sensitizers.

The potential distribution at the semiconductor/solution interface under weak depletion and accumulation conditions were investigated. The applied potential is partitioned between the space charge layer in the semiconductor and the Helmholtz layer on the solution side of the interface. Under deep depletion conditions, a change in the applied potential usually appears across the space charge layer and the band bending can be determined using the Mott-Schottky relation. Under conditions of weak depletion, determination of band bending is not straightforward.

A study was conducted to analyze the sol-gel synthesis of carbon/ceramic composite electrodes with an interconnected network of carbon particles. Films of the silica-based gel featured pore sizes smaller than 1 micron. Experimental results indicated that the electrodes were porous and electrically conductive. Findings also showed that more than half of the carbon surface area was accessible electrochemically.

A numerical model is proposed that obtains the electrical output of dye-sensitized solar cells from microscopic parameters. The current-voltage curve, the dependence of the short-circuit current and the open-circuit voltage on the light intensity are determined within the assumptions of the model.

The synthesis of ZnO nanoparticles from Zn(CH3CO2)(sub 2), ZnBr2, and Zn(ClO4)(sub 2) in 2-propanol is reported. The rate constant for coarsening at constant temperature increases in the order of Br(super -) < CH3CO2(super -) < ClO4(super -) indicating that the rate is dependent on anion adsorption.

The growth kinetics of TiO2 nanoparticles synthesized from aqueous solution is reported using titanium(IV) isopropoxide as precursor. It was found that the number of primary particles per secondary particle increases with time, and the percentage of primary particles present in the colloid decreases with increasing temperature.

The pseudohalogens redox couples are evaluated to determine the effect of the equilibrium potential of the redox couple on the energetics and kinetics of dye-sensitized TiO2 photoelectronchemical cells. The results revealed that selecting a redox couple with a more positive equilibrium potential does not necessarily translate into an increase of the open circuit potential.

The mechanisms of particle growth for four oxides and oxyhydroxides from homogenous solution, which consist of hematite (Fe2O3) synthesized by aging an acidic ferric chloride solution, feroxihite (FeOOH) by oxidation of a ferrous chloride solution, anatase (TiO2) by sol-gel synthesis and hydrothermal aging, and heterogenite (CoOOH) by oxidation of cobalt (II) chloride solution is examined. Findings suggest that the aggregation processes dominate the solution-based growth of several metal oxide / oxyhydroxide particles.

An important reason for the relatively low efficiency of dye-sensitized solar cells (DSSCs) is the low open-circuit voltage ( V OC ) of about 0.7 V for a standard solar cell with a dye that has an absorption onset at 1.6 eV. We report an enhancement of the V OC of about 0.10 V with respect to a TiO 2 -based DSSC modified with ZnO nanoflowers that we prepared by a new and facile method. An additional increase of the V OC of about 0.08 V was achieved by modifying the ZnO nanoflowers with Au nanoparticles, resulting in a DSSC with an efficiency of 2.79%, highlighted by a high V OC of 0.89 V. Detailed analysis with electrochemical impedance spectroscopy and intensity-modulated photovoltage and photocurrent spectroscopies (IMVS and IMPS) reveal that the main reason for the increase of V OC is related to the shift of the band edges upon coupling TiO 2 with ZnO nanoflowers, even though the electron lifetime at the same charge density actually decreases. These results show the intricate interplay between band edge shift, recombination kinetics, and DSSC performance and illustrate that a higher voltage DSSC can be fabricated by modification of the photoanode materials., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

The presence and deteriorating action of microbial biofilms on historic stone buildings have received considerable attention in the past few years. Among microorganisms, fungi are one of the most damaging groups. In the present work, antimicrobial surfaces were prepared using suspensions of Ca(OH)2 particles, mixed with ZnO or TiO2 nanoparticles. The antimicrobial surfaces were evaluated for their antifungal activity both in the dark and under simulated natural photoperiod cycles, using Penicillium oxalicum and Aspergillus niger as model organisms, and two limestone lithotypes commonly used in construction and as materials for the restoration of historic buildings. Both Ca(OH)2-ZnO and Ca(OH)2-TiO2 materials displayed antifungal activity: ZnO-based systems had the best antifungal properties, being effective both in the dark and under illumination. In contrast, TiO2-based coatings showed antifungal activity only under photoperiod conditions. Controls with coatings consisting of only Ca(OH)2 were readily colonized by both fungi. The antifungal activity was monitored by direct observation with microscope, X-ray diffraction (XRD), and scanning electron microscopy (SEM), and was found to be different for the two lithotypes, suggesting that the mineral grain distribution and porosity played a role in the activity. XRD was used to investigate the formation of biominerals as indicator of the fungal attack of the limestone materials, while SEM illustrated the influence of porosity of both the limestone material and the coatings on the fungal penetration into the limestone. The coated nanosystems based on Ca(OH)2-50%ZnO and pure zincite nanoparticulate films have promising performance on low porosity limestone, showing good antifungal properties against P. oxalicum and A. niger under simulated photoperiod conditions.

We report on the synthesis of ZnO particles from Zn(CH(3)CO(2))(2) in 2-propanol as a function of the concentration of water, in the absence of a base such as NaOH. Particles with diameters of 3-5 nm are formed depending on time, temperature, and water concentration. The nucleation and growth are slower than in the presence of NaOH, and at longer times the increase in particle size is dominated by diffusion-limited coarsening. The rate constant for coarsening increases with increasing water concentration up to 150 mM, above which the rate constant is 1.1 x 10(-4) cm(3) s(-1), independent of the water concentration. The width of the particle size distribution decreases with increasing water concentration, and at 250 mM water, the full width at half-maximum of the distribution function is essentially the same as for the synthesis of ZnO using NaOH as a reactant. The temperature dependence of coarsening is determined by the bulk solubility of the ZnO nanoparticles and yields an apparent activation energy of 1.12 eV. This is significantly larger than the activation energy of 0.35 eV for coarsening of ZnO from 1 mM Zn(CH(3)CO(2))(2) in 2-propanol with 1.6 mM NaOH.

Dye-sensitized mesoporous nanocrystalline SnO2 electrodes and the pseudohalogen redox mediator (SeCN)2/SeCN- or (SCN)2/SCN- or the halogen redox mediator I3-/I- were implemented for regenerative solar cell studies. Adsorption isotherms of the sensitizers Ru(deeb)(bpy)2(PF6)2, Ru(deeb)2(dpp)(PF6)2, and Ru(deeb2(bpz)(PF6)2, where deeb is 4,4'-diethylester-2,2'-bipyridine, dpp is 2,3-dipyridyl pyrazine, and bpz is bipyrazine, binding to the SnO2 surface were well described by the Langmuir model from which the saturation coverage, Gamma0 = 1.7 x 10(-8) mol/cm2, and surface-adduct formation constant, Kad = 2 x 10(5) M(-1), were obtained. Following excited-state interfacial electron transfer, the oxidized sensitizers were reduced by donors present in the acetonitrile electrolyte as shown by transient absorption spectroscopy. With iodide as the donor, a rate constant k > 10(8) s(-1) was measured for sensitizer regeneration. In regenerative solar cells, it was found that the incident photon-to-current conversion efficiencies and open circuit voltages (Voc) were comparable for (SeCN)2/SeCN- and I3-/I- for all three sensitizers. The Voc varied linearly with the logarithm of the short circuit photocurrent densities (Jsc), with typical correlations of approximately 50-60 mV/decade. Capacitance measurements of the SnO2 electrode in the presence of I3-/I-, (SeCN)2/SeCN- or (SCN)2/SCN- are reported.